Oven control systems



T- L. HENSON OVEN CONTROL SYSTEMS Dec. 30, 1969 Filed Dec. 21, 1967 4Sheets-Sheep 1 m v w 7 Iv m um \mm m r y Q N i k .2 Q M N t \m\ u 5 Pi I|-W 4 eumdwm S M T/ Gama W NN $501 I v? m Q INN W MN /v a S ll l I 1 I aI I l T l fiT x Aw s ST wl M EDQQQSQWIB T. L. HENSON OVEN CONTROLSYSTEMS 4 Sheets-Sheet 2 Dec. 30, 1969 Filed Dec. 21, 1967 Dec.30, 1969'r. HENSON 3,486,694

OVEN CONTROL SYSTEMS- Filed Dec. 21, 1967 4 Sheets-Sheet 5 MOE five 760/45 4550.? flfltvlv 14m fiawn, 6 MM ,arrae/virs Dec. 30, 1.969 T. L.HENSON 3,486,694

OV'EN CONTROL SYSTEMS Filed Dec. 21, 1967 4 Sheets-$heet 4 INVENTORTHOMAS LESLIE HENSON United States Patent US. Cl. 236- 26 ClaimsABSTRACT OF THE DISCLOSURE An oven control system, which includes meansfor sensing the moisture content and/ or colour of a product leaving theoven and for controlling the oven so that the product has a desiredmoisture content and/ or colour, means being provided for detecting theabsence of a product leaving the oven and thereupon exerting Ian indpendent control over the oven.

This application is a continuation-in-part of my pending applicationSer. No. 633,615, filed Apr. 25, 1967, now abandoned, for Oven ControlSystems, which is accorded the priority date of Great Britain patentapplication 8,666 filed Mar. 2, 1964, and a continuation-in-part of myco-pending application, Ser. No. 434,195, filed Feb. 23, 1965, nowabandoned for Oven Control Systems, which is accorded the priority dateof Great Britain patent application No. 7,196 filed Feb. 18, 1966.

This invention relates to oven control systems, for the purpose ofcontinuously controlling the treatment of a product passing through anoven, such as a bakers oven, in order to obtain desired characteristicsof the treated product.

The present invention consists in a control system for an oven, whichincludes sensing means for sensing the moisture content and/or colour ofa product emerging from the oven, the moisture content and/ or colour ofthe product being dependent upon the heat treatment efiected by theoven, means for controlling the heat treatment carried Out by the ovenin accordance with the moisture content and/or colour sensed by thesensing means in order to achieve a desired moisture content and/orcolour of the product, and means for detecting the absence of a productemerging from the oven in order to exert an independent control over theheat treatment in the absence of a product.

The expression colour as used in the specification is intended toinclude the tone or shade of a particular colour, so that where, forexample, a product changes from light brown to dark brown under theinfluence of the heat treatment, the system will function to maintainthe product emerging from the area at the correct desired tone or shadeof brown. Conversely, it is not necessary that the system should be ableto sense a change to a completely different colour which would never beencountered during the operation of the system. With the aid of filtersthe system may be rendered especially sensitive to slight changes fromthe desired colour.

In the accompanying drawings:

FIGURE 1 shows diagrammatically one form of system according to thepresent invention;

FIGURE 2 shows in more detail the color sensing means used in FIGURE 1;

FIGURE 3 is a side elevation of a mounting for the colour sensing meansof FIGURE 2;

3,486,694 Patented Dec. 30, 1969 "ice FIGURE 4 is a cross section takenon line 4-4 of FIG- URE 3;

FIGURE 5 shows means for detecting the presence or absience of a productfor use in the system of FIGURE 1; an

FIGURE 6 is a diagrammatic view of an oven and a control systemtherefor.

In carrying the invention into effect according to one convenient modewherein colour is sensed by way of example, the invention will bedescribed with reference to an oven for baking Swiss roll sponge whereina continuous strip or carpet of Swiss roll batter is conveyedcontinuously through the oven, each portion of the strip or carpet ofbatter progressively changing in state as it progresses through the ovenuntil a certain final colour of the Swiss roll sponge is obtained oncompletion of the process as each portion leaves the oven.

A control system is provided for the oven in which colour sensing meansare arranged to sense the final colour of the product and to cause forexample a change of temperature, position of dampers, speed of conveyorin the oven or like adjustment, in order to ensure that as the strip orcarpet leaves the oven it is the correct desired colour.

As shown in FIGURE 1, the colour of the sponge 1 emerging from agas-fired oven 2 is sensed by a photoelectric cell3 which is positionedadjacent the discharge end of the oven and which is adapted to scanacross the width of the conveyor band. The photoelectric cell 3 isarranged to produce an output voltage which is dependent upon the colourof the baked Swiss roll sponge emerging from the oven. This outputvoltage is fed to an indicator and control device 4 and thence through aswitch 5 to a power supply 6 which controls a servomotor 7 which, inturn, controls a valve 8 governing the supply of gas through a headerpipe 9 to the burners of the oven 2.

In this way, the colour of the Swiss roll sponge emerging from the gasfired oven is maintained approximately constant, any slight changes fromthe desired colour being rapidly and automatically corrected by anappropriate change in the supply of gas to the burners, although equallyeifective correction may be obtained by a change in the speed of theconveyor band, in the position of dampers or a like adjustment.

Suitable means are provided in the circuit of the control device 4 foradjusting the condition at which the system is stable, and this adjustedcondition of the colour is maintained by the system. An alarm circuit isprovided so that if the system detects a considerable departure from thedesired colour, due for example to a fault, the alarm will be raised tocall for attention by an operator.

In order to deal with a gap which may occur between the trailing edge ofone length of Swiss roll sponge and the leading edge of the next, or todeal with the situation when no Swiss roll sponge is passing through theoven, detecting means in the form of a capacitative proximity detector10 are arranged adjacent the colour sensing means 3 to detect theabsence of Swiss roll sponge at this point.

When such an absence is detected, the change of capacitance at thedetector 10 is arranged to actuate a relay 11 which in turn energizes awinding 12 controlling the changeover switch 5 which disconnects theservomotor 7 from the colour control and connects it to a temperatureindicator control device 13 which is connected to a thermocouple 14associated with the interior of the oven 2 so that the fuel supply tothe oven, and thus its temperature, are temporarily controlled to adesired temperature determined by the temperature control circuit. Assoon as the detecting means 10 detects further Swiss roll sponge, thechangeover switch 5 is actuated again and the control of the fuel supplyis once again governed by the colour sensing means.

In order to prevent the detecting means 10 from hunting a time delaydevice is provided so that in the event of short gaps appearing on theoven band, the changeover switch is not actuated. Thus in the case ofthe production of bread, biscuits, and the like, which products arenormally spaced apart on the conveyor band, the changeover switch 5 willnot be operated until there is a definite break in the production.

FIGURE 2 shows in more detail the color sensing means 20 which includesa housing 21 containing a lowvoltage electrical lamp 22, and an opticalsystem, including lens 24 for focusing a beam 25 of light upon a productshown diagrammatically as at 27.

Light is reflected and scattered back from the product 27 onto anannular photocell 28. Since the intensity of the reflected light dependsupon the colour of the product, the electrical output from the photocell28 will give an indication of the colour of the product 27.

For the purpose of calibration, a white tile 29 is mounted so that itcan be temporarily moved to the position shown in dash lines in FIGURE 2to reflect light directly back onto the photocell 28 which thus gives astandard reference output for adjustment purposes.

FIGURES 3 and 4 show a mounting for causing the colour sensing means 20to be reciprocated transversely to scan the entire width of the band 33carrying the products from the oven.

The sensing means 20 is secured to a casing 34 supported by rollers 35between fixed parallel rails 36. The sensing means 20 and the casing 34can be driven from one end of the rails 36 to the other (i.e.,transversely of the band 33) by means of an electrical motor 37 locatedin the casing 34 and which drives, through a speed reduction gear 38, apinion 39 meshing with a rack 40 formed on the underneath edge of one ofthe rails 36.

The supply cables to the motor 37 and to the lamp 22 of the sensingmeans 20 pass through flexible conduit 41, and the supply to the motoris reversed, to cause reciprocation of the sensing means 20 and casing34, at adjustable points determined by selected ones of the limitswitches 42 which cooperate with a trip arm 43 on the casing 34.

The whole apparatus is protected from heat radiated from the band 33 andthe products carried on it by a heat shield 44 having a transverse slot45 through which the sensing means 20 may scan the product on the band33.

In FIGURE 5 there is shown the proximity detector 10. Under normalworking conditions a plate 51 is disposed parallel to and spaced fromthe band 33 and forms with the band 33 and associated circuitry aproximity detector to indicate whether or not a product is present onthe band 33 beneath the plate 51.

However, the plate 51 secured to arms 52 is mounted for movement about apivot 53 on a horizontal axis carried on a fixed bracket 54 so thatshould the plate be engaged by a lump in the product, the plate 51 willswing upwardly to the position shown in phantom and avoid damage.

Various alternative detecting means can be used to signal a changeoverfrom standard thermocouple temperature control to automatic control ofcolour, as for example by inductance, radiation, sonic beams and thelike. The detecting means can also be incorporated with the coloursensing means such that upon a signal received by the colour sensinghead being outside the desired colour range, the changeover switch isactuated.

Indicators may be associated with the control circuits to indicate theoperating and desired (preset) values of colour and oven temperature.

In the case of employing turbulent ovens, i.e. forced convection heat,the colour sensing means may also control the weight of air beingrecirpulated in the oven chamber,

In carrying the invention into effect according to another convenientmode by way of example wherein both moisture content and colour aresensed, the accompanying drawing, FIGURE 6, shows diagrammatically anoven 101 for baking Swiss roll sponge wherein a continuous strip orcarpet 102 of Swiss roll batter is conveyed on an endless belt 103continuously through the oven, each portion of the strip or carpet 102of batter progressively changing in state as it progresses through theoven until a certain final moisture content and colour of the Swiss rollsponge is achieved on completion of the process as each portion leavesthe oven.

A control system is provided for the oven which includes a computer 104arranged to receive signals from sensing means arranged to sense thefinal state or condition of the product and in turn signals if necessaryfor a change in the various operating conditions of the oven in order toensure that as the strip or carpet leaves the oven it is the correctdesired moisture content and colour, which are two major requirements inthe baked product.

The sensing means 105 for sensing the moisture content of the Swiss rollsponge at the discharge end of the oven, consists of an electrodeworking as a variable capacitance in accordance with the moisturecontent of the adjacent sponge. A similar moisture content sensingdevice 106 is positioned at the entrance to the oven. The colour of thesponge is sensed by a photoelectric cell 107 which is positionedadjacent the moisture content sensing means 105 and which is adapted toscan across the width of the conveyor band. The photoelectric cell 107is arranged to produce an output voltage which is dependent upon thecolour of the baked Swiss rolls emerging from the oven and which is fedto the computor 104. The humidity inside the oven is measured by ahumidity indicator 108 which sends an output signal to the computor 104.In the indicator 108 a continuous sample is taken of the ovenatmosphere, heated to a predetermined temperature, passed through oneorifice, cooled so that all the moisture condenses, passed through asecond orifice at supersonic speed, and then pumped into the atmosphere.

The oven 101 is provided with gas burners 109 controlled by controlvalves 110 located in a gas input control panel 111 which also includeschange over switches 112 arranged so that the valves 110 are controlledeither directly by the computor 104 or by temperature controllers 113connected to temperature sensitive elements 114 located in the oven, andto the computor 104. The changeover from one control to the other willbe explained more fully hereinafter.

The oven is also provided with a turbulence fan 115, an extraction fan116, turbulence ports 117, and a main control panel 118 for starting upthe oven before the computer takes over control.

The computer 104 is arranged to control motorized turbulence (forcedconvection) control dampers 119, a steam injection control valve 120controlling steam injectors 121 for increasing the humidity in the ovenand a motorized extraction damper 122 for decreasing the humidity in theoven. The computor 104 is also arranged to control a device 123 forregulating the speed of the oven conveyor band 103 and a panel 124comtrolling the ingredients of the mix for the sponge.

The sponge mix is prepared by feeding its ingredients through meters 125controlled by panel 124 to a mixer 126 and thence to a sponge depositer127 located adjacent the entrance to the oven.

The colour and moisture of the sponge can be influenced by the followingfactors:

(a) The humidity within the baking chamber of the oven,

(b) The temperature Within the baking chamber,

(c) The amount of turbulence or forced convection in the ove (d) Thetime each portion of the sponge spends in the oven, i.e. theoven-conveyor speed, and

(e) The ingredients and nature of mixing.

The computor 104 is arranged to control the above factors in thefollowing way:

(i) The humidity may be increased by controlled steam injection, ordecreased by controlled extraction,

(ii) The temperature within the baking chamber may be controlled by theburner control valves 110,

(iii) The amount of turbulence may be controlled by the dampers 119.

(iv) The time in the oven may be controlled by the speed regulatingdevice 123, and

(v) The ingredients and nature of mixing may be controlled by themetering devices 125, and the type and time of mixing employed (e.g.ingredients heated, or cooled under pressure, 01' in vacuum and soforth).

Any of the above corrections to the operating conditions may take placesimultaneously with others under the control of the computor 104.

In this way, the moisture content and colour of the Swiss roll emergingfrom the gas fired oven is maintained approximately constant, any slightchanges from the desired moisture content and colour being rapidly andautomatically corrected by an appropriate change in the supply of gas tothe burners, speed of conveyor band, position of dampers or likeadjustment.

Suitable means are provided in the moisture content and colour controlcircuits for adjusting the conditions at which the system is stable, andthis adjusted condition of the moisture content and colour is maintainedby the system.

In order to deal with a gap which may occur between the trailing edge ofone length of Swiss roll sponge and the leading edge of the next, or todeal with the situation when no Swiss roll sponge is passing through theoven, detecting means 128 in the form of a photoelectric cell and lampfor example, or a capacitative proximity detector, are arranged adjacentthe colour sensing means 107 to detect the absence of Swiss roll spongeat this point.

When such an absence is detected, a signal is fed to the computor 104which in turn actuates the changeover switches 112 which disconnect thegas control valves 110 from the direct control of the computor inaccordance with the moisture content and colour and connects the valves110 to the temperature controller 113, the fuel supply to the gasburner, and thus the oven temperature is temporarily controlled to adesired temperature determined by the temperature control circuit which,in turn, is controlled by the computor to suitable preset temperatures.As soon as the detecting means detects further Swiss roll sponge, thechangeover switches are actuated again and the control of the fuelsupply is once again governed by the computor in accordance withmoisture content and colour sensing means.

It is to be noted that to prevent the detecting means from hunting atime delay is provided such that in the event of short gaps appearing onthe oven band, the changeover switches are not operated, but will beoperated for longish breaks in the baking of Swiss roll sponge. However,when considering the production of bread, biscuits, sponges and thelike, which products are normally spaced apart on the conveyor band, thefrequency of the signal to the detecting means can be used to determinewhether or not the changeover switch is actuated.

Various detecting means can be used to signal a changeover from standardthermocouple temperature control to automatic control of temperature,moisture content and colour, as for example by capacitance, inductance,radiation, sonic beams and the like. The detecting means can also beincorporated with the moisture content sensing means such that upon asignal received by the moisture content sensing head being outside thedesired moisture content range, the changeover switch is actuated.

Indicators may be associated with the control circuits to indicate theoperating and desired (preset) values of moisture content, colour andoven temperature.

In the case of employing turbulent ovens, i.e. forced convection heat,the moisture content and colour sensing means may also control theweight of air being recirculated in the oven chamber.

The sensing means arranged to measure the moisture content of the stripor carpet of batter before it enters the oven feeds this information tothe computor so that in the event of a change in the moisture content ofthe batter entering the oven the computor can signal for a suitableadjustment to compensate for it.

Various modifications may be made within the scope of the presentinvention.

I claim:

1. A control system for an oven having an oven chamber, which includesmeans for moving a product such as bread dough in a path of travelthrough the oven chamber, means for sensing the condition of a productemerging from the oven chamber, means mounting said sensing means inspaced relation with said product for to-and-fro movement transverselyacross the said path of travel, and means for controlling the heattreatment effected by the oven chamber in accordance with the conditionsensed by the sensing means in order to achieve a desired condition ofthe product.

2. A system as claimed in claim 1, wherein means are provided fordetecting the absence of a product emerging from the oven chamber.

3. A system as claimed in claim 1, wherein the controlling meansincludes means for controlling the temperature of the oven chamber inaccordance with the colour sensed by the sensing means.

4. A system as claimed in claim 1, wherein the condition sensing meansincludes a photoelectric cell arranged to receive light from the productemerging from the oven chamber.

5. A system as claimed in claim 4, wherein the colour sensing means alsoincludes a lamp and an optical system for directing light from the lamponto the product emerging from the oven.

6. A system as claimed in claim 4, wherein the condition sensing meansalso includes a member having a standard reference colour which can betemporarily positioned to reflect light upon the photoelectric cell forcalibration purposes.

7. A system as claimed in claim 1, wherein the condition sensing meansis carried upon a carriage mounted upon rails, the carriage beingreciprocated from one end of the rails to the other by means of anelectrical motor.

8. A system as claimed in claim 1, wherein the absence of a productemerging from the oven chamber is detected by a proximity detectorarranged adjacent the exit of the oven chamber.

9. A system as claimed in claim 1, wherein detecting means is arrangedto actuate a change-over switch, in the event of the absence of aproduct, and thereby disconnect the condition controlling means andconnect means for sensing the temperature of the oven chamber to exert acontrol upon the oven temperature.

10. In association with an oven having means for conveying a productthrough the oven and means for regulating the temperature of the oven, acontrol system which includes means for sensing the condition of theproduct emerging from the oven, means operatively conmeeting saidsensing means to said regulating means whereby the condition of theemerging product is main tained at a predetermined level, means formeasuring the temperature of the oven, means for detecting the absenceof a product emerging from the oven, and means for disconnecting saidsensing means from said regulating means and connecting said temperaturemeasuring means to said regulating means in the event of the detectionof the absence of a product by said detecting means.

11. A control system for an oven, which includes means for sensing thecolour of a product emerging from the oven, the colour of the productbeing dependent upon the heat treatment of the oven, means forcontrolling the heat treatment effected by the oven in accordance withthe colour sensed by the sensing means in order to achieve a desiredcolour of the product, and means for exerting an independent controlover the oven temperature in the absence of a product emerging from theoven, the colour sensing means including a photoelectric cell arrangedto receive light from the product emerging from the oven, and thephotoelectric cell being of annular form and surrounding a beam of lightfrom the lamp to the product.

12. A control system for an oven which includes means for sensing thecondition of a product emerging from the oven, the condition of theproduct being dependent upon the heat treatment of the oven, means forcontrolling the heat treatment effected by the oven in accordance withthe condition sensed by the sensing means in order to achieve a desiredcondition of the product, means for exerting an independent control overthe oven temperature in the absence of a product emerging from the oven,detecting means arranged to actuate a changeover switch, in the event ofthe absence of a product, and thereby disconnect the conditioncontrolling means and connect means for sensing the temperature of theoven to exert a control upon the oven temperature, and a time delaydevice arranged to delay operation of the changeover switch so thatsmall gaps in the product are ignored.

13. A control system for an oven, which includes: means for moving aproduct such as bread dough in a path of travel through the oven; meansfor sensing the condition of a product emerging from the oven; meansmounting said moving means for to-and-fro movement transversely acrossthe said path of travel; means for controlling the heat treatmenteffected by the oven in accordance with the condition sensed by thesensing means in order to achieve a desired condition of the product;and means for detecting the absence of a product emerging from the oven.

14. A system as claimed in claim 13 wherein the capacitor is mounted forpivotal movement about a horizontal axis so that it can move upwardly ina direction away from the product in the event of a larger portion ofproduct being encountered.

15. A control system for an oven having an oven chamber, which includesmeans for sensing the condition of a product emerging from the ovenchamber, the condition of the product being dependent upon the heattreatment of the oven chamber, means for controlling the heat treatmenteffected by the oven chamber in accordance with the condition sensed bythe sensing means in order to achieve a desired condition of theproduct, and means responsive to a temperature affected condition of theoven chamber atmosphere for exerting an independent control over theoven chamber temperature in the absence of a product emerging from theoven chamber, the absence of a product emerging from the oven chamberbeing detected by a proximity detector arranged adjacent the exit of theoven chamber, the proximity detector including a capacitor plate locatedimmediately above the product emerging from the oven chamber.

16. A system as claimed in claim 19, wherein means are also provided forsensing the colour of a product emerging from the oven, the colour ofthe product being dependent upon the heat treatment effected by theoven, and means for controlling the heat treatment carried out by theoven also in accordance with the colour sensed by the colour sensingmeans in order to achieve a desired colour of the product,

17. A system as claimed in claim 16, wherein further sensing means areprovided for sensing the. moisture content of a product entering theoven, and means for controlling the heat treatment carried out by theoven also in accordance with the moisture content sensed by he furthermoisture sensing means.

18. An oven for the treatment of discrete products comprising conveyormeans for conveying the product through the oven: treatment meansregulating the condition of the oven and affecting the product withinthe oven, the condition of the treated product depending upon thetreatment exerted by said treatment means; a control system whichincludes means for sensing the condition of the product emerging fromthe oven, means for controlling the treatment exerted by said treatmentmeans upon the product in accordance with the condition sensed by thesensing means in order to achieve a desired condition of the product,and means for detecting the absence of a product and exerting anindependent control over said treatment means in the absence. of theproduct.

19. A control system as set forth in claim 18 wherein the means forsensing the condition of the product includes means for sensing themoisture content of the product.

20. A system as claimed in claim 19, wherein the means for controllingthe heat treatment carried out by the oven includes means forcontrolling the humidity within the oven.

21. A system as claimed in claim 19, wherein the means for controllingthe heat treatment carried out by the oven includes means forcontrolling heating means associated with the oven.

22. A system as claimed in claim 19, wherein the. means for controllingthe heat treatment carried out by the oven includes means forcontrolling the amount of turbulence or forced convection.

23. A system as claimed in claim 19, wherein the means for controllingthe heat treatment carried out by the oven includes means forcontrolling the time taken for a product to pass through the oven.

24. A system as claimed in claim 19, wherein means are provided forcontrolling the preparation of a product fed to the oven for heattreatment by the oven in accordance with the nature of the productarriving at and/or leaving the oven.

25. In association with an oven for the heat treatment of productshaving means for conveying a product through an oven chamber, thecondition of the treated product depending upon the treatment exerted bythe oven, an oven chamber, a control system which includes means forsensing the condition of the product emerging from the oven chamber,means for controlling the heat treatment exerted by the oven chamberupon the product in accordance with the condition sensed by the sensingmeans in order to achieve a desired condition of the product, means fordetecting the absence of a product emerging from the oven chamber andexerting an independent control over the oven chamber temperature inresponse to a temperature affected condition of the oven chamberatmosphere and in the absence of the product; and time delay means forde laying operation of said latter means so that small gaps in the flowof product are ignored.

26. A control system for an oven, which includes means for sensing thecondition of a product emerging from the oven, the condition of theproduct being dependent upon the heat treatment of the oven, means forcontrolling the heat treatment effected by the oven in accordance withthe condition sensed by the sensing means in order to achieve a desiredcondition of the product, means for exerting an independent control overthe oven temperature in the absence of a product emerging from the oven,detecting means arranged to actuate a change-over switch, in the eventof the absence of a product, and thereby disconnect the conditioncontrolling means and connect means for sensing the. temperature of theoven to exert a control upon the oven temperature, and a time delaydevice ar- 9 10 ranged to delay operation of the change-over switch 801,980,816 11/ 1934 McDill 340-258 X that small gaps in the product are.ignored. 2,025,542 12/1935 Lugar 236-15 2,674,809 4/ 1954 Meienhofer34-48 References Clted 2,724,903 11/1955 Ehrism-an 73-73 X UNITED STATESTS 5 3,124,430 3/ 19 64 'Eicken 73-73 X 8/1965 Sawyer et a1. 236 15 X3,332,279 7/1967 Tompos et a1. 73-73 7/1935 73455 X WILLIAM E. WAYN-ER,Primary Examiner 8/1950 Knlveton 263-3 2/1951 =Swain 236-15 8/1963 Ha73-3ss x 8 1930 G di 99 331 73-169, 356; 99-331; 107-55; 236-46, 78;340-258

